7 AXIS CNC MACHINING: HIGH ACCURACY & FLEXIBILITY

Need parts with the highest quality and precision but within the shortest possible lead time? You need 7 Axis CNC Machining. It is the leading-edge technology in the multiaxis machining industry.

In this article, we have tried to focus on different important parameters of 7-axis CNC machining. I hope this will help you enhance your knowledge of 7-axis CNC machining.

Sunrise Metal specialized in aluminum die casting and CNC precision machining manufacturing. We produce high-precision aluminum alloy parts with high-accuracy CNC machining equipment. If you have any inquires or demands, Sunrise will be here for serving you.

Types of 7 Axis Machines

There are different types of 7-axis CNC equipment available. Typically, 7-axis CNC machines are classified into two categories. They are,

• Machining Center
• Robot

The machining center and the robot arm are completely different in how they look and function. When people talk about seven-axis CNC machining, they mostly refer to robots.

However, CNC machining centers can have the seven-axis capability as well. We will be discussing both the CNC machining centers and robots in this article.

7 Axis CNC Machining Milling

Normally, a 5 axis CNC machining center will be enough for machining very complex parts with minimum or no setup changes. So, why need a 7 axis machine?

Well, it’s not just about being able to machine the complex most parts. There are other important aspects such as speed, quality, repeatability, etc. that should be considered as well.

Structure

7 Axis CNC machining center is your traditional CNC machining center, but with 7 axis capabilities. They are more efficient at handling the workpiece. Machining centers made by different manufacturers may have different assemblies.

The tool setup and work holding may slightly differ from each other. But, the most common type is a 7 axis CNC milling & turning center. It serves the purpose of both a milling machine and a lathe. And it has interchangeable or separate milling and turning tools.

It will usually have two spindles that act as additional rotating axes for the machine. So, it adds more flexibility to the process.

Working Principle

7 Axis CNC machining centers are capable of both milling and turning. This eliminates the time wasted between tool change and workpiece handling. Although, it is possible in a 3 axis machining center or 4 axis machining center as well. But it has a very limited capacity to handle complex parts.

7 Axis CNC machining center eliminates this issue. It can machine very complex parts like a 5 axis CNC machine. And the additional 2 axis movement of tools makes the entire process more efficient through complete automation.

The two-spindle has a chuck to clamp and rotate the workpiece. This allows working from different angles and carry out turning operations. Both spindles can work simultaneously for turning parts, or individually for turning with one and removing completed parts with another.

Due to the multitasking capabilities, complete automation can be achieved with a 7-axis CNC machine. And manufacturers can design and program the parts with any CAD, CAM software, and generate g-codes to feed into the CNC machine.

Here’s is a video of a 7-axis CNC milling and turning center in action that features complete machining of a part from scratch.

Material Support

7 Axis CNC Machining Centers can deal with all sorts of material. Their high rigidity and resistance to vibration allow them to deal with very hard materials as well.

• Steel
• Aluminum
• Brass
• Copper
• Plastic, etc.

A lot of other materials can be machined with it as well. But, manufacturing with seven-axis CNC machines can be costly. So, it is not usually preferred for dealing with relatively soft materials as there are cheaper alternatives.

Workspace

7 axis CNC machining centers have a confined workspace with limited capacity. They are suitable for machining small to medium-sized parts. Average-sized machining centers can fit parts with a volume up to 1-2 cubic feet at best.

So, when you have huge things to machine, a machining center may not be the best option. However, there are bigger CNC machines available as well for machining very large parts. Such machines can cost a fortune and have a very high production cost.

Big industries like the automotive and aerospace will afford large CNC machining centers. But, small businesses don’t usually need machining at such a scale. Most of their machining demands should be met by an average-sized 7 axis CNC machining center.

Precision

When we are talking about the quality and precision of parts, nothing beats a 7 Axis CNC Machining Centers. Machining centers are highly optimized to ensure extremely tight tolerance thus excellent repeatability for parts.

The machining center allows better work handling and calibration. Due to the absolute positioning of the tools and spindles, identifying and adjusting the coordinates is easier. So, there are fewer chances for errors.

Also, 7 axis CNC machining centers have very high rigidity and stiffness. So, they can negate the effect of vibration and resistance when machining hard materials like steel. It allows them to maintain tight tolerances when machining hard materials.

7 Axis CNC Machining Robots

It is an articulated robot with 7 axis movement and machining capabilities. They are also known as 7 axes industrial robots or robot arms. Up until now, robot arms mainly been used for the automation of different industrial processes such as product handling, welding, assembling, etc.

However, there has been a recent rise in the trend of using robots for milling. They are very convenient and offer many unique benefits that are not achievable by regular CNC machines.

Structure

The structure of seven Axis CNC robots is completely different than a seven-axis machining center. all 7 axes are utilized in the movement of the robot.  And you also can achieve additional degrees of freedom through a rotating table which further increases its productivity.

Manufacturers mount the seven-axis CNC robot on a rotating table or a rail that allows it to move from one place to another. The rail mechanism is very useful for dealing with massive projects such as prototyping automobiles or huge sculptures.

The main body of the seven-axis robot arm is divided into multiple segments. The joints allow rotational and linear movement of these segments. So, the whole body can fold to reach close locations or extend to reach a point far away.

Working Principle

7 axis CNC robots are capable of 360-degree rotation at multiple joints. So, they are incredibly flexible and are able to access any location of a part. Still, a turntable is installed to minimize the robot arm movement and fasten the process.

A simple turntable with one-axis rotation will significantly increase the efficiency of machining. The need for workpiece setup changes is almost eliminated with 7-axis CNC machining. And manufacturers can nearly machine any design in one go regardless of the complexity.

Programming a 7 axis CNC machining robot is not the as same a regular CNC machine. Robots usually can’t be programmed using G-codes as different robot manufacturers use their preferred programming language for robots.

Popular CAM software such as Autodesk PowerMILL has plugins for dealing with 7-axis robot milling. Third-party tools or robot manufacturer-provided software packages are available as well which can help you convert machine codes (G-codes) into robot codes.

Here is a video that provides a short overview of programming a 7-axis CNC robot milling machine using the Autodesk PowerMILL.

Material Support

7 Axis CNC Robot has lower stiffness and rigidity compared to a machining center. So, trying to machine hard materials will result in excess vibration in the machine. This causes deviation from the toolpath during machining and compromises the precision of parts.

Most of the 7 axis milling robots manufactured till now are capable of dealing with relatively soft materials such as,

• Plastic
• Wood
• EPS foam
• Resin
• Marble, etc.

Steel and harder varieties of aluminum alloy will be difficult to machine using a 7 axis CNC robot. However, robot manufacturers are working on making them more stable to deal with more sophisticated materials.

Workspace

Unlike machining centers, 7 axis CNC robots are not confined and have a very large workspace. Manufacturers usually keep the robot along with the turntable in an open space. Even a medium-size robot arm is capable of machining things as large as 8 cubic feet.

Automotive industries even create full-size automobile prototypes using 7-axis robots mounted on rails. This way you can customize 7-axis robots to machine enormous prototypes and sculptures.

However, machining large parts with tight tolerances is only possible with soft materials like wood, plastic, foam, etc.  CNC robots’ lack of stiffness and rigidity makes it difficult to machine large metal parts.

Precision

7 Axis CNC robots are hard to program and calibrate. Unlike machining centers, robots don’t have absolute coordinates. The workpiece and tool head of robots needs to be calibrated very carefully using CMM devices.

But readjusting it for a different design may seem like a hassle. It is hard to calibrate it to a precision level that is achievable by a machining center. And robots have lower stiffness and rigidity. So, they are prone to vibration when machining hard materials. The vibration compromises the precision achievable by a 7 axis CNC robot. However, they are capable of maintaining reasonably high precision when dealing with soft materials.

Which One to Pick?

Both 7-axis CNC machining center and 7-axis CNC robots have some excellent features but their scope of application is very different. To choose the right 7 axes CNC machine you should have a clear idea of what you are trying to achieve.

• 7-axis CNC machining is widely used for rapid prototyping. When you are aiming for functional prototypes, machining centers will be better. Robots will be more efficient when you need a visual prototype of your final product.
• 7-axis CNC robot machining is very useful for architectural projects where visual appearance has maximum importance. Robots are capable of handling extremely complex designs.
• The machining center is ideal for manufacturing small to medium-sized metal parts and very high precision can be obtained. CNC Robot is ideal for machining small to massive blocks made out of relatively soft material.
• The precision of machining metal with a 7-axis CNC robot will not be as close as a machining center. So, if you need metal parts, the machining center will be a better option.
• Machining large parts of the same material will be more cost-effective with a 7-axis CNC robot. But, do keep in mind the material restrictions.
• A machining center is more suitable for the mass production of parts. While a robot is good for dealing with a single project like a prototype or sculpture.
• The programming and calibration of CNC robots are more difficult. This will compromise the quality of parts unless handled very carefully. So, when precision is of prime importance, a machining center will be more convenient.